MOSCOW -- Russia identified NATO as the nation's No. 1 military threat and raised the possibility of a broader use of precision conventional weapons to deter foreign aggression under a new military doctrine signed by President Vladimir Putin on Friday. NATO flatly denied it is a threat to Russia, and accused Moscow of undermining European security. The new doctrine, which comes amid tensions over Ukraine, reflected the Kremlin's readiness to take a stronger posture in response to what it sees as U.S.-led efforts to isolate and weaken Russia. The paper maintains the provisions of the previous, 2010 edition of the military doctrine regarding the use of nuclear weapons. It says Russia could employ nuclear weapons in retaliation for the use of nuclear or other weapons of mass destruction against the country or its allies, and also in the case of aggression involving convention...